(1) Field of the Invention
This invention relates to semiconductors and, more particularly, to semiconductor structures and methods of using the same.
(2) Prior Art
In known alternators for automobiles, the full wave rectifier associated with the alternator typically takes up a substantial portion of the volume of the alternator. This is both because of the structure of the components of the rectifiers and the need for having a sufficiently large cooling surface. Cooling is a sufficiently important problem that automobile alternators typically have fans for forcing air through the alternator.
A typical prior art rectifier makes use of individually mounted and packaged semiconductor diodes which are then wired to form the full wave rectifier. A typical mounting for each diode is a "can" which is a generally cup-shaped metal housing wherein is positioned a piece of preformed solder, a semiconductor diode chip, another piece of preformed solder and an external connection. The open end of the can is sealed so that the external connection extends out of the can. There is sufficient internal space in the can to allow for expansion and contraction of the lead. Typically, the cost of the functional element, the semiconductor chip, is a relatively small fraction of the total cost of the can. That is, the packaging accounts for a substantial portion of the total cost of each can.
Another method of packaging a semiconductor rectifier chip is in the "button" form. A pair of conductive leads having flatten ends each abut preformed solder connections which contain therebetween the semiconductor chip. By heating this construction, the solder flows and connects the semiconductor chip to the leads. The entire assembly is then coated in epoxy to seal the interior. With the "button" construction as with the aforementioned "can" construction, the package contains only one semiconductor rectifier chip. Thus, further fabrication is necessary to assemble these chips into a rectifier suitable for use with an alternator.
Various other prior art structures are known for mounting semiconductor rectifier chips. For example, it is known to start with a ceramic base, mount the semiconductor chip on the ceramic base and then cap the semiconductor chip so thate is an air space on one side of the semiconductor chip. The structure has a disadvantage in that air is a poor heat conductor and most of the heat generated within the semiconductor chip must be dissipated through the ceramic base. Typically, in an automobile environment, it is difficult for such an arrangement to provide sufficient heat dissipation.
It would be desirable to have a simple full wave rectifier structure which is easily fabricated and readily cooled. These are some of the problems this invention overcomes.